The present invention relates to a change device for a continuously operating reel up of a paper machine, the change device being arranged in connection with a reel spool which functions as the core for a new roll of paper. The present invention also relates to a method for changing a roll in a continuous reel-up of a paper machine.
In the reel-up for a paper web, in a so-called Pope-type reel-up, or a centre-drive-assisted Pope-reel, the ready-made paper is reeled after the calender around a reel spool (reeling drum). The reeling itself is conducted in such a way that the reel spool is loaded against a reeling cylinder over which the web to be reeled travels, winding around the reel spool to form a complete roll or reel.
Also this section of the paper machine has to operate in a non-stop manner and receive the continuous paper web passed from the preceding sections of the paper machine. Thus, when the old roll is complete, the web has to be cut off, after which the next stage is to start winding the web following the cut-off point around a new reel spool. In practice, this takes place in such a way that when the paper reel has reached its full size, a new empty reel spool, i.e. a reeling drum is moved to the surface of the reeling cylinder in contact with the paper web, and after that the paper web is cut off in a suitable way, and the web end following the cut-off point is guided onto the circumference of the empty reel spool, on which a new roll starts to accumulate.
The most critical stages of the reeling are the cutting off of the paper web and bringing the new end of the web around the empty reel spool. In order to avoid excess broke, the change has to take place without problems. In an ideal case, the new end of the web is brought immediately neatly against the circumferential surface of the empty reel spool. As is well known, there are several ways for conducting the cutting and the exchange, depending on the grammage. One way is to utilize the speed difference between the complete paper reel and the reeling cylinder to produce a web loop, which is guided to the empty reeling drum, whereupon the web is broken. Another method is to feed a special cutting ribbon in the nip between the reeling cylinder and the empty reeling drum, wherein it, when entrained by the reeling drum, simultaneously cuts off the web coming to the reeling cylinder and guides the new end of the web around the reeling drum. The exchange of the roll can also be conducted by cutting the web after the nip between the reeling cylinder and the empty reeling drum, for example by means of an air blowing and by guiding the web around the reeling drum.
At present, paper machines generally run at the speed of 20 m/s or faster, and the aim is, of course, to attain even higher speeds. The cutting of a fast running web is not a problem as such, and the forces due to the speed can even be utilized in the cutting. The critical point is to bring the end of a new web immediately against the circumferential surface of the reeling drum and to make it follow the surface at a high peripheral speed and to prevent the web from wandering in an uncontrolled manner or being displaced on the reeling drum. This problem becomes worse when the grammage is increased.
The purpose of the present invention is to provide a reliable change device of a reel-up, suitable for changing a roll especially at high running speeds of the web and/or with heavy paper grades. In an advantageous manner, according to the invention, the web wound on the reeling drum is subjected to air jets substantially over the full width of the web, which air jets guide the web around the machine reel and also act within a sector of suitable size to bring the web around this reeling drum. The air jets are advantageously generated by providing the guiding device according to the invention with air jet nozzles. In this way it is possible in a contactless manner to guide the leading end of the web, winding on a new reeling drum, in an area of a predetermined length in the circumferential direction, until the web is wound sufficiently around the reeling drum so that the web will follow this leading portion and wind around the reeling drum, starting to form superimposed layers.
The air jets can for example be positioned and directed in such a way that they press the web against the surface of the reeling drum and are effective within a sufficiently long sector in order to hold the web against the surface of the reeling drum, or they guide the web along a web guide surface arranged to guide the web around a new reeling drum. The flow rate of the air jets is adjustable, and it can be advantageously adjusted at least as high as the production rate of the machine, i.e. the travel speed of the web.
The method of present invention relates to a method for changing a roll in a continuous reel-up of a paper web, in which the web running onto an old roll is cut off and is guided onto a reel spool forming the core of the new roll, the leading end of the web being guided onto the reel spool by means of airjets.
The travel of the leading end following the cut-off point of the web can be guided in various ways by means of air jets effective substantially over the full width of the web opposite to the reeling drum.